In his Tractatus de haereticis of around 1330, the judge-advocate Zanchino Ugolini wrote that his work was needed because inquisitors were ignorant of the laws that governed their actions: ‘inquisitores, ut plurimum, sunt iuris ignari’. Indeed, in pleading to be excused of his temerity in striking down a predecessor's verdict, the inquisitor Lorenzo d'Ancona confessed as much. The person who was meant to keep the inquisitor's actions legal was the inquisition notary. He and his small group of colleagues were probably the most important members of the inquisitor's direct team, since they were essential for the validation of any kind of business in medieval Italy. Transactions recorded by a qualified notary were ‘public instruments, whose authority did not depend on witnesses, seals or other authenticating devices’ but simply on the notary's own declaration. Where notaries were appointed under authority of either emperor or pope, the authenticity and accuracy of the documents they prepared or copied was recognised both universally and long after the death of the originator. Locally accredited notaries had a more restricted range of recognition outside their home area, but were still essential to validate local business.

Notaries swore to record faithfully the subject matter with which they were dealing, and could be struck off or subjected to other penalties if they failed to observe their oath. Their participation not only attested the veracity of judicial proceedings and records of public business, but also gave weight to commercial and financial contracts of all kinds. Yet Andrea del Col wrote as recently as 2010 that ‘the characteristics, responsibilities and activity of inquisition notaries are poorly understood’.

The importance attached by the inquisition to written records has frequently been commented on, but it was the notary himself who gave them authenticity. Public belief about the notary's significance in inquisition business is attested very early, when in 1249 four suspected heretics in Orvieto kidnapped the notary of the inquisitor Ruggiero Calcagni, along with his registers, and forced him to rewrite the acts concerning them. By falsifying the record of which he was custodian, they (rather naively) supposed they would escape punishment. Solvi comments that ‘the attempted falsification of the register [seems to me to show] full awareness of the irreplaceable juridical value of the records of the processes’.